Regulated hydrogen-to-naphtha mol ratio



May 28, 1963 J. K. SINGER REGULATED HYDROGEN -TO-NAPHTHA MOL RATIO 5 Sheets-Sheet 1 Filed Feb. 24, 1961 Chorge- Prefreoted Mid- Continent Nophthu 103 Octane 500 PSIG ILHSV REACTOR #I REACTOR #2 REACTOR #3 Tons of Cofolysr |0,000 Bbl/S-D.

INVEN'TOR.

y 8, 1963 J. K. SINGER 3,091,584

REGULATED HYDROGEN -TONAPHTHA MOL RATIO Filed Feb. 24, 1961 s Sheets-Sheet 2 C +H av/er 5rab/7izer Age/7f y 28, 1963 J. K. SINGER 3,091,584

REGULATED HYDROGEN -TONAPHTHA MOL. RATIO Filed Feb. 24, 1961 3 Sheets-Sheet 5 3,091,534 REGULATED HYDROEEN-TO NAPHTHA MOL R TIO Joe Kenneth Singer, Norwallr, Conn, assignor to Socony Mobil Oil Company, Inc, a corporation of New York Filed Feb. 24, 1961, Ser. No. 91,465 4 Claims. (til. 208-65) The present invention relates to upgrading naphtha having a low octane rating to provide a gasoline having an octane rating higher than the charge naphtha, and, more particularly to reforming naphtha in the presence of particle-form solid platinum-group metal reforming catalyst.

The literature and the patents pertinent to reforming naphtha to produce reformate having a higher octane .rating than the charge stock are replete with information concerning the use of hydrogen to reduce the deposition of a carbonaceous residue designated coke generally. To achieve this purpose the practitioners in the art recommend that the naphtha be reformed in the presence of hydrogen in mol ratios of from one to twenty mols of hydrogen per mol :of naphtha. It is common practice to separate reformer gas comprising hydrogen and hydrocarbons having one to three carbon atoms in the molecule, usually designated C to C hydrocarbons, from the reformate comprising hydrocarbons having four and more carbon atoms in the molecule, usually designated (3 or C and heavier hydrocarbons. However, in order to control the vapor pressure of the finished gasoline the C and heavier reformate is debutanized to provide (3;, and heavier reform-late with which the separated butanes are mixed in the volume required to provide gasoline having the required vapor pressure.

The major portion of the aforesaid reformer gas comprising hydrogen and C to C hydrocarbons is recycled to the reforming reactors to provide the aforesaid hydrogen necessary to control the deposition of coke.

More recently, it has been disclosed that improved results can be obtained when reforming naphtha by contacting the naphtha in a first reforming reactor or stage under reforming conditions with the minimum amount of catalyst to produce a maximum difference between the temperature of the vapors entering and leaving the aforesaid first reforming reactor or stage (U.S. Patent No. 2,946,737). The patentee recommends that the charge naphtha be reformed in the presence of hydrogen employing the aforesaid reformer recycle gas in the mol ratio of about four to fifteen mols of hydrogen per mol of naphtha. In other words, the mol ratio of hydrogen in the recycle gases to the naphtha charged to the reactors is within the limits of four to fifteen, preferably six to ten, mols of hydrogen per mol of naphtha. That is to say, this patentce, like the others skilled in the art recommends that the hydrogen-to-naphtha ratio in all of the reforming reactors be the same. On the other hand, it has now been discovered that improved yields can be obtained when the hydrogen-to-naphtha mol ratio is regulated in each reforming reactor or stage.

It is generally postulated that at least four reactions take place and are competing when naphtha containing naphthenes and paraffins is reformed. (Aromatic hydrocarbons are relatively stable and may be considered inert at the usual catalytic reforming temperatures and pressures.) These four reactions are grossly illustrated by the following equations:

( l) Naphthenes:anomatid[-H (2) Paraflin:naphtheneI-}-H (3) Parafiin +H elighter paraffins (cracking) (4) Normal paratfinciiso-parafiin It will be observed that postulated Reactions 1 and 2 produce hydrogen. However, in the present method only the hydrogen entering each reactor in the recycle gas is regulated.

However, regulating the hydrogen-to-naphtha mol ratio cannot be divorced from other variables affecting the reforming reactions. That is to say, the concentration of naphthenes in the charge naphtha and the heat input to an adiabatic reactor cannot be ignored.

The variation in the concentration of naphthenes in virgin naphtha is well illustrated by the low naphthene content of Kuwait naphtha illustrative of Mid-Eastern naphthas, the median concentration of naphthenes in Mid-Continent virgin naphthas, and the high concentration :of naphthenes in California Virgin naphthas. The compositions of these illustrative naphthas are given in Table I.

Table I Kuwait Mid- Calif. Cont Total 100. 00 100. 00 100. 00

In general, the effect of reducing the recycle ratio, i.e., the hydrogen-to-naphtha, mol ratio in all of the reforming reactors or stages from 10:1 to 6:1 when reforming Mid-Continent virgin naphtha, i.e., straight run naphtha, is to reduce substantially the advantageous effect of catalyst distribution on the yield of product. This is illustrated in Table II.

1 Octane rating of 05+ reiorrnate (EH-3 cc. TEL) =103.

It will be observed that when reforming Mid-Continent virgin naphtha containing 45.6 percent naphthenes at a hydrogen-to-naphtha mol ratio of 10 to 1 the yield of (1 rotor-mate is increased by 2.5 percent when the catalyst fill of the first reactor is reduced from 18.7 tons to 3.7 tons, i.e., is reduced to a minimum to produce a maximum difference between the temperature of the vapors entering and leaving the first adiabatic reactor or stage. On the other hand, when the recycle ratio, i.e., the hydrogen-to-naphtha rnol ratio is contemporaneously reduced from 10 to 1 to 6 to l the yield at the three catalyst distributions is substantially the same or somewhat better for equal amounts of catalyst in each reactor or stage.

In contrast, when reforming a naphtha having a higher concentration of naphthenes, such as California virgin naphtha, the recycle ratio has no effect on the product distribution at reforming severities to produce C and heavier reformate having octane rating (R+3 cc. TEL) within the range of 97 to 102. However, at overall liquid hourly space velocity of 0.68, i.e., at a total catalyst fill of 82 tons per 10,000 barrels of naphtha charged per day, when producing C and heavier reformate having an octane rating (R+3 cc.) of 109 the yields of the aforesaid reformate are two to three per cent higher for six to one than for ten to one hydrogen-to-naphtha mol ratio. This 18 clearly evidenced by the illustrative data presented in Table III.

Table III Catalyst distribution, 05+ reformate tons/10,000 BID Overall Hydrogenliquid to naphtha hourly mol ratio space (recycle Percent Octane R1 R2 R3 velocity ratio) of rating charge (11-1-3 co.

TEL)

The effect of recycle ratio and catalyst distribution upon the yield of C reformate from naphtha of relatively low naphthene concentration, e.g., Kuwait virgin naphtha is illustrated by the data presented in Table IV.

Table IV Catalyst distribution, 05+ reiormate tons/10,000 BID Overall Hydrogenliquid to naphtha hourly mol ratio space (recycle Percent Octane R R R3 velocity ratio) of rating charge (R+8 cc.

TE L) The data presented in Tables II, HI and IV establish that for virgin naphthas or in general naphthas having a low concentration, i.e., less than thirty volume percent of naphthenes, the effect of recycle ratio is negligible. On the other hand, for naphthas having naphthene concentrations within the range of thirty to fifty percent by volume the recycle ratio, i.e., the hydrogen-to-naphtha ratio should be at least 10. When reforming naphthas containing more than fifty percent of naphthenes by volume to produce C reformates having octane ratings in excess of 102 it is advantageous to reduce the recycle ratio to about 4 to 6 mols of hydrogen per mol of naphtha.

While the data presented in Tables II, III, and IV have been obtained from reforming operations in which the ratio of hydrogen-to-naphtha in all reactors or reforming stages have been the same the present method provides for regulating the hydrogen-to-naphtha mol ratio at least in the first reactor or stage and, preferably, in both the first and the second reforming reactors or reforming stages. In other words, in those reactors or stages in which the predominating reaction is dehydrogenation the recycle ratio is lower than the recycle ratio in the reactors in which other reforming reactions take place. For practical purposes the recycle ratio in those reactors in which the temperatures of the vapors at the outlet of the reactor is lower than the temperature of the vapors at the inlet of the same reactor are those reactors in which the volume of the hydrogen which is introduced into the reactor is in a mol ratio to the naphtha feed to the first reactor within the range of about four to about seven mols of hydrogen per mol of original naphtha feed.

Such a change from the usual practice of introducing all of the hydrogen into the first reforming stage or the first reforming reactor in a plurality of reforming reactors piped for series flow of the vaporous reactants and products of the reactions requires no extensive change in the piping of the unit. The only change is that of substituting a recycle manifold with a valved branch to each reforming stage or reactor for the conduit from the recycle gas compressor to the naphtha feed heater. This is readily visualized by those skilled in the art after inspection of the drawing FIGURE 2.

Illustrative of another embodiment of the present invention is FIGURE 3 wherein the flow of gases and liquids through a reforming unit employing four reactors R R R and R is schematically depicted. In FIGURE 3 reactors R and R each are charged with reforming catalyst in the proportion of about 3 tons per 10,000 barrels of naphtha charged to the unit per day while reactors R and R each are charged with reforming catalyst in the proportion of about 15 to 16 tons per 10,000 barrels of charge stock introduced into the unit per day. The hydrogen-to-naphtha mol ratio in reactors R and R is 3 to 7 mols of hydrogen per mol of naphtha. In reactors R and R the hydrogen-to-naphtha mol ratio is at least 8. Accordingly, it is an object of the present invention to regulate the hydrogen-to-naphtha ratio in each reforming stage to provide in those stages wherein the temperature of the vapors at the outlet of the stage is at least ten degrees Fahrenheit lower than the temperature of the vapors at the inlet of the aforesaid stage with a hydrogen-to-naphtha mol ratio based upon the volume of the original liquid feed which is lower than the hydrogen-to-naphtha mol ratio in the reforming stages in which the temperature of the vapors at the outlet of the stage is equal to or higher than the temperature of the vapors at the inlet of the aforesaid stage. It is another object of the present invention to also regulate the hydrogen-to-naphtha mol ratio in those stages in which, while the temperature of the vapors at the outlet of the stage is higher or equal to the temperature of the vapors at the inlet to the aforesaid stage, the temperature of the vaporous reactants at some point between the vapor inlet and the vapor outlet is at least ten degrees Fahrenheit lower than the temperature of the vapors at the inlet to the aforesaid stage. This latter situation is illustrated by FIGURE 1 of the drawings which is a set of three graphs of the temperature profile of three adiabatic reformers each filled 'with the same quantity of particleform solid platinum-group metal reforming catalyst, e.g., comprising 0.6 percent by weight of platinum and 0.7 percent by weight of chlorine on an alumina support.

The graph of FIGURE 1 for reactor 1 shows that there is a drop of about eighty-five degrees Fahrenheit from the temperature of the vapors at the inlet of reactor I to the outlet of reactor 1. In reactor 2 the drop in temperature between the vapor inlet and the vapor outlet is only about eighteen degrees. On the other hand, the vapor outlet temperature of reactor 3 is higher than the temperature at the vapor inlet of reactor 3. Those skilled in the art recognize that these numerical values each are subject to change dependent upon the naphthene content of the charge naphtha, the liquid hourly space velocity and the severity of the reforming conditions. Nevertheless, in general, the vapor outlet temperature of each of the first two reactors of a three reactor (adiabatic) unit is lower than the vapor inlet temperature of each reactor while the vapor outlet temperature of the third reactor is higher than the vapor inlet temperature of the third reactor. Thus, it can be said that the present method provides for admixing hydrogen with the hydro carbon charge to each reactor or reaction stage in which the predominating reaction is an endothermic reaction, for example, the dehydrogenation of naphthenes, in a lower mol ratio than the mol ratio in which hydrogen is mixed with the hydrocarbon charge to the reactor or reactors in which the predominant reaction is an exothermic reaction, e.g., hydrocracking. For facility of industrial operations all hydrogen-to-naphtha mol ratios are based upon the liquid charge to the first reactor or reaction stage. The mol ratio of hydrogen-to-naphtha for each reactor in a plurality of reactors, e.g., three, is illustrated in the following tabulation:

Table V Charge rate: 10,000 b./d., i.e., 417 bjhr. Recycle gas purity:

70 percent hydrogen 30 percent C1 to C4 hydrocarbons Reactor Reactor Reactor Predominant types of reaction No. 1 No. 2 No. 3

Endothermic Exothermic Exothermic Mols hydrogen/mol naphtha 4-6 8-20 8-20 Bbls. teed/hour 417 417 217 Mols feed/hour 884 884 084 Mols hydrogen/hour 3 540-5, 300 8, 840 8, 840 MSCF hydrogen/hour 1,416-2, 120 3, 536 3, 536 MSCF recycle gas/hour 2, 023-3, 035 5,050 5, 050

Reactor Reactor Reactor Iredominant types of reaction No. 1 No. 2 N o. 3

Endothermic Endotherlnic Exothermic Mols of hydrogen/mol naphtha. 4-0 4-6 10 Bbls. feed/hour 41 417 :17 Mols feed/hour 884 884 84 Mols hydrogenlhoun. 3, 540-5, 300 3, 540-5, 300 8, 840 MSCF hydrogen/hour 1, 416-2, 120 1, 416-2, 120 3, 536 MSCF hydrogen/hour" 2, 023-3, 035 2, 023-3, 035 5, 050

1 MSGF is thousand standard cubic feet.

Illustrative of the flow of liquids and gases through a reformer unit comprising three reactors is the flow sheet in FIGURE 2. (Those skilled in the art will recognize that several heat exchangers not pertinent to the inventive concept of the present invention have been omitted for the purpose of simplifying the drawing and the description.) For the purpose of the description of the present invention the treatment of virgin, i.e., straight run naphtha having a naphthene content of about 45 percent by volume of naphthenes is illustrated in FIGURE 2. Thus, naphtha containing an amount of sulfur which can be tolerated by the steel of the equipment, usually not more than about 20 ppm. (parts per million) of sulfur, not more than 1 ppm. of nitrogen, and not more than 1 p.p.b. (part per 10 parts) of arsenic and preferably essentially free of arsenic is the feed to the reforming unit. (As used herein essentially free of arsenic designates a concentration of arsenic in a reformer feed which, when said reformer feed is contacted with a bed of reforming catalyst comprising 0.35 percent platinum by weight, is sufficient to deactivate said catalyst within the life of the catalyst, for example, two years, as determined by other factors such as the temperature required to produce a reformate having an octane rating of at least 100 (R-l-B cc.), the yield of reformate, and the mechanical strength of the catalyst.) The aforesaid concentrations of sulfur, nitrogen, and arsenic are designated innocuous concentrations of sulfur, nitrogen and arsenic. The aforesaid reformer feed or charge naphtha or charge stock is drawn through pipe 1 by pump 2 from a source not shown. Pump 2 discharges the charge naphtha into conduit 3 at a pressure in excess of that existing in reformer 7 (R The charge naphtha flows through conduit 3 to coil 4 in heater 5. At a point in conduit 3 intermediate to pump 2 and to heater hydrogen-containing gas (after start-up reformer recycle gas) flowing from compressor 26 through recycle manifold 27 and manifold branch 31 under control of valve 32 is mixed with the charge naphtha to provide a charge mixture. Since the reaction in reactor 7 (R which predominates is an endothermic reaction, the hydrogen-containing gas is mixed with the charge naphtha in proportions to produce a charge mixture in which the mol ratio 6 of hydrogen-to-charge naphtha is within the range of about 4 to 6 mols of hydrogen per mol of charge naphtha.

The charge mixture flows through conduit 3 to coil 4 in heater 5. In heater 5 the charge mixture is heated to reforming temperature dependent upon the activity of the catalyst, the target or required octane rating of the leaded gasoline to be produced, i.e., the octane rating of the C and heavier reformate to be produced, and the liquid hourly space velocity. [Hereinafter, the C and heavier reformate is designated C reformate. All octane ratings given herein are those obtained by the research method with leaded naphtha containing 3 cubic centimeters of tetraethyl lead and characterized as octane rating or octane number (R-i-3 cc.).]

Reforming conditions are within the limits set forth in Table VI.

From heater 5 the heated charge mixture flows through conduit 6 to reformer R or reactor 7. In reactor 7 the charge mixture is contacted with particle-form solid platinum-group metal reforming catalyst, for example, a particle-form reforming catalyst comprising about 0.35 to about 0.6 percent by weight of platinum and about 0.4 to about 0.7 percent by weight of chlorine on a refractory oxide support such as alumina. Reforming conditions in reactor 7 are within the limits set forth hereinbefore.

In the drawing reformers R R and R or reactors 7, 12 and 17 are symbolic of adiabatic reactors. On the other hand, the first reactor can be operated under what is designated as isothermal conditions. Such isothermal conditions are not classic isothermal conditions in view f the fact that in many instances the temperature of the vapors leaving the first reactor is ten to twenty degrees lower than the temperature of the vapors entering the reactor. Furthermore, in accordance with some descriptions of methods of reforming naphtha, e.g., oopending application for United States Letters Patent Serial No. 731,138, now abandoned, the temperature of the vapors entering the first reactor initially is higher than the initial temperature of the vapors entering the second and third reactors. Accordingly, when the first reactor is operated under pseudoor quasi-isothermal conditions the first reactor efiluent in some instances need not be reheated to reforming temperature. Similarly, when the first reactor is an adiabatic reactor the temperature of the first reactor effiuent can be as high or higher than the predetermined temperature of the vapors entering the second reformer (R That is to say, the vapor inlet temperature at the second reformer can be the same as, higher or lower than the temperature of the first reformer efiiuent. Consonant with the foregoing, the efliuent of the first reformer (reactor 7) flows through conduit 8 to coil 9 in heater 10 or by-passes coil 9 and flows directly to reactor 12. (Bypass not shown.)

It is also to be observed that in accordance with the disclosure in US. Patent No. 2,946,737 the first reactor can contain the minimum amount of catalyst to produce the maximum difference between the temperature of the vapors at the inlet and the temperature of the vapors at the outlet of the first reactor.

In reactor 7 the heated vaporous charge mixture flows downwardly under reforming conditions of temperature and liquid hourly space velocity in contact with platinumgroup metal reforming catalyst to the outlet of reactor 7. From the outlet of reactor 7, when the vapor inlet temperature of reactor 12 is higher than the vapor outlet temperature of reactor 7, the first reactor effluent flows through conduit 8 to coil 9 in heater It). Since the predominant reaction in reactor 12 is endothermic the hydrogen-tonaphtha mol ratio in reactor 12 is within the limits of 3 to 7. Furthermore, since the charge mixture entering reactor 7 contained hydrogen in the hydrogen-to-naphtha mol ratio of 4, and since the hydrogen-to-naphtha mol ratio in the first reactor eflluent is at least 4, it is unnecessary to admix hydrogen or hydrogen-containing gases with the first reactor efiluent. Accordingly, valve 349 remains closed and substantially no reformer recycle gas flows from manifold 27 through manifold branch 29.

On the other hand, instead of establishing a charge mixture in which the hydrogen-to-naphtha mol ratio is 6, for example, hydrogen or hydrogen-containing gas such as reformer recycle gas can be mixed with the charge naphtha to provide a charge mixture in which the m l ratio of hydrogen-to-naphtha is 3 and additional hydrogen or hydrogen-containing gas, e.g., reformer recycle gas, mixed with the eflluent of the first reactor to make the hydrogen-to-naphtha mol ratio 6 at the vapor inlet of the second reactor. In these circumstances valves 32 and 30 are adjusted to admit hydrogen or reformer recycle gas from manifold 27 to both conduit 3 and conduit 8.

In the event that the predominant reaction in the second reactor '-(12) is exothermic suificient hydrogen-containing gas, e.g., reformer recycle gas, flows from manifold 27 through manifold branch 29 under control of valve 36 to make the hydrogen-to-naphtha mol ratio (based upon mols of feed naphtha) at the vapor inlet of the second reactor. Under these conditions, valve 33 in conduit 28 is closed and substantially no reformer recycle gas flows through manifold branch 28. The foregoing is sum- The finst reactor effluent, also designated first effluent, with or without added hydrogen or hydrogen-containing gases {as illustrated) flows through conduit 8 to coil 9 in heater 10. In heater 10 the first reactor effluent is reheated to reforming temperature the same as or higher, or lower than the vapor inlet temperature at the first reactor (7). The heated first reactor effluent flows from heater 10 through conduit 11 to the second reactor 12. The heated first reactor effluent flows downwardly in contact with platinum-group metal reforming catalyst the same as or different from the platinum-group metal reforming catalyst in the first reactor to the outlet of reactor 12. The efiluent of the second reactor, designated second efiduent, flows from reactor 12 through conduit 13 to coil 14 in heater 15. When the hydrogen-to-naphtha mol ratio in the second efiluent is less than 10, sufiicient hydrogen or hydrogen-containing gases, such as reformer recycle gas, flows from manifold 27 through manifold branch 28 under control of valve 33 to raise the mol ratio of hydrogen-tonaphtha to at least 10 based upon the mols of charge stock.

In heater 15 the second effluent is heated to reforming temperature the same as, lower than, or higher than, the vapor inlet temperature at the finst reactor (7). The heated second efi luent flows from heater 15 through conduit 16 to the third reactor 17. In reactor 17 the heated second efi luent flows downwardly to the outlet of reactor 17 in contact with platinum-group metal reforming catalyst having the same as or difierent from the composition of the reforming catalyst in reactors 7 and 12.

From reactor 17 the third reactor effluent, designated final effluent, flows through conduit 18 to cooler 19. In cooler 19 the final effluent is cooled to a temperature at which, under the existing pressure, C and heavier, i.e., C hydrocarbons are condensed. The cooled final effiuent flows from cooler 19 through conduit 20 to liquidgas separator 21. In liquid-gas separator 21 the condensed (3 hydrocarbons are separated from reformer gascomprising hydrogen and C to C hydrocarbons.

The separated C hydrocarbons, designated final condensate, flow from separator 21 through pipe 22 to stabiliz'mg, storage, blending, distribution, admixing of additives, such as alkyl leads, anti-icers, and the like finishing operations.

The reformer gas comprising hydrogen and C to C hydrocarbons separated from the final condensate in separator 21 flows therefrom through conduit 23 to compressor 26. At a point intermediate to separator 21 and to compressor as, a portion of the reformer gas, usually substantially equal in volume to the gas made in reactors '7, l2, and 17 is diverted through conduit 24 under control of valve 25 to other processes employing gas of substantially the composition of the reformer gas or to the refinery fuel main. The balance of the reformer gas, sufiicient to provide at least 10 mols of hydrogen per mol of charge naphtha flows through conduit 23 to compressor 26. Compressor 26 recompresses the reformer gas, designated reformer recycle gas or recycle gas, to a pressure at least substantially the same as the pressure in c011- duit 3. Compressor 26 discharges the reformer recycle gas or recycle gas into recycle gas manifold 27 for distribution as described hereinbefore.

The flow of gases and liquids through a reforming unit employing two small reactors and two conventionally sized reactors is illustrated in FIGURE 3. (Those skilled in the art Will recognize that several heat exchangers not pertinent to the inventive concept of the present invention have been omitted for the purpose of simplifying the drawing and the description.) Thus, charge stock containing not more than innocuous (as defined hereinbefore) concentrations of sulfur, nitrogen and arsenic is drawn from a source not shown through pipe 51 by pump 52. Pump 52 discharges the charge stock into conduit 53 at a pressure greater than the pressure in reactor 56. The charge stock flows through conduit 53 to heater 54. At a point in conduit 53 intermediate to compressor 52 and heater 54 hydrogen-containing recycle gas flowing from compressor 74 through recycle gas manifold 79 and manifold branch 77 under control of valve '78 is mixed with the charge stock to provide a charge mixture comprising hydrogen and naphtha in the mol ratio of 3:1. The charge mixture flows through conduit 53 to heater 54. In heater 54 the charge mixture is heated to provide a vapor inlet reforming temperature at reactor 56 in the range set forth hereinbefore in Table VI. From heater 54 the charge mixture at reforming temperature flows through conduit 55 to reactor 56. For the purpose of illustration reactor 56 is charged with platinum-group metal reforming catalyst in the proportion of about 3 tons per 10,000 barrels of charge stock treated per day, i.e., about 22.24 barrels of catalyst per 417 barrels of charge stock treated per hour. The charge mixture flows downwardly through reactor 56 to the outlet thereof. The effluent of reactor 56, designated first effluent, flows from reactor 56 through conduit 57 to 9 heater 58. In heater 58 the first effluent is reheated to provide at reactor 66 a vapor inlet reforming temperature the same as, higher than, or lower than the vapor inlet reforming temperature at reactor 56. The heated first effluent flows from heater or furnace 58 through conduit 59 to reactor 64 Reactor 64) is charged with about 22.24 barrels or 3 tons of platinum-group metal reforming catalyst having substantially the same composition or a different composition as the platinum-group metal catalyst charged to reactor 56. The reheated first effluent flows downwardly through reactor 69 to the outlet thereof. The effluent of reactor 61 designated second effluent, flows from reactor 6t) through conduit 61 to heater or furnace 62. At a point in conduit 61 intermediate to reactor 60 and heater 62 hydrogen-containing recycle gas flowing from compressor 74 through manifold 79 and manifold branch 86 under control of valve 81 is mixed with the second effluent in amount to provide a hydrogen-to-naphtha rnol ratio of 6. The second charge mixture resulting therefrom flows to furnace 62. In heater 62 the second charge mixture is heated to a temperature to provide at the vapor inlet of reactor 64 a vapor inlet reforming temperature the same as, higher than, or lower The uncondensed third effluent, designated reformer gas, flows from separator 72 through conduit 73. A portion of the reformer gas, usually a volume about equivalent to the gas made in reactors 56, 60, 64-, and 68, i.e., the make-gas, is diverted through conduit 75 under control of valve 7 6 to other hydroprocesses, i.e., processes using hydrogen of the same or greater purity. The balance of the reformer gas, designated recycle gas, flows through conduit 73 to compressor 74.

The condensate of the final efiluent, designated final condensate, comprising C and heavier hydrocarbons flows from separator 72 through pipe 84 to stabilizing, storage, blending, distribution, admixing of additives, such as alkyl leads, anti-icers, and the like finishing operations.

It will be observed that the catalyst distribution, liquid hourly space velocity, and hydrogen-to-naphtha mol ratios used for illustrative purposes hereinbefore are as follows and are compared with the catalyst distribution, liquid hourly space velocity, and hydrogen-to-naphtha rnol ratio for prior art methods of reforming as typified by that disclosed in U.S. Patent No. 2,946,737 in Table VIII.

Table VIII Present invention Prior art Total Reactor designation R1 Ra Ra R4 R1 R2 Ra Tons of catalyst per 10,000 barrels/day--- 3. 0 3.0 3. 4 17.0 17.0 Bbls. catalyst 22. 24 22. 24 25. 3 126. 3 126. 4 Percent of total catalyst 8 8 9.1 45. 4 45. 5 Liquid hourly space velocity 18.8 18. 8 16 3.3 3.3 Overall liquid hourly space velocity 5. 5 1. 5 1. 5 1. 5 1. 5 I-Iydrogen-to-naphtha rnol ratio 3 3 10 10 10 Octane number (R+3 00) 05+ reformate 102 102 102 102 102 than the vapor inlet temperature at reactor 56. From heater 62 the heated second charge mixture flows through conduit 63 to reactor 64. Reactor 64 is charged with about 15.7 tons or 116.76 barrels of platinum-group metal reforming catalyst of substantially the same or different composition as that in reactors 56 and 60 per 10,000 barrels of naphtha treated per day. The second charge mixture flows downwardly through reactor 64 to the outlet thereof. The efiluent of reactor 64, designated third effluent, flows from reactor 64 through conduit 65 to heater or furnace 66. At a point in conduit 65 intermediate to reactor 64 and heater 66 hydrogen-containing recycle gas flowing from compressor 74 through manifold 79 and manifold branch 32 under control of valve 83 is mixed with the aforesaid third effluent to provide a third charge mixture comprising hydrogen and C and heavier hydrocarbons in the hydrogen-to-naphtha rnol ratio of 10. In heater 66 the aforesaid third charge mixture is heated to provide a vapor inlet reforming temperature at reactor 68 the same as, higher than, or lower than that at reactor 56. From heater 66 the third charge mixture flows through conduit 67 to reactor 66.

Reactor 68 is charged with about 116.76 barrels or 15.7 tons of platinum-group metal reforming catalyst of substantimly the same or different composition as the catalyst in reactor 56 per 10,000- barrels of naphtha treated per day. The heated third charge mixture flows downwardly through reactor 63 to the outlet thereof. The effluent of reactor 68, designated final effluent, flows from reactor 68 through conduit 69 to cooler 70.

In cooler 70 the final effiuent is cooled to a tempera- L re at which C and heavier hydrocarbons are condensed at the existing pressure. From cooler 70 the uncondensed final effluent comprising hydrogen and C to C hydrocarbons and the condensate comprising C and heavier hydrocarbons flows through conduit 71 to gasliquid separator 72. In gas-liquid separator 72 the uncondensed final eflluent separates from the condensate.

Those skilled in the art will recognize that the foregoing descniption is that of la reforming process or method employing a plurality of reactors or reaction Zones, with reheating of at least the effluent of all reaction zones except the first prior to introduction of the efiluent into the succeeding reactor and when the temperature of the eflluent of the first reaction zone, i.e., the first effluent, is below the reforming temperature required at the inlet of the second reaction zone, also reheating the first effluent to the aforesaid required reforming temperature. In the present method the reforming conditions of temperature and liquid hourly space velocity are those required to produce 0 reformate having the required or target octane dependent upon the activity of the catalyst employed, The present invention comprises admixing with the charge naphtha, i.e., charge stock, an amount of hydrogen or hydrogen-containinzing gases to provide a charge mixture having a hydrogen-to-charge naphtha rnol ratio of at least three and not more than seven, maintaining a hydrogen-lto-naphtha rnol ratio of at least three and not more than seven while the predominant reaction is an endothermic reaction, i.e,. while the temperature of the effluent of a reaction zone is lower than the temperature of the reactants entering the aforesaid reaction zone, i.e., until the charge naphtha has contacted at least the first about 15 to about 70 percent of the total catalyst in all of the reaction zones, by the admixing of hydrogen or hydrogen-containing gases such as reformer recycle gas. Thereafter, i.e., after the predominant reaction ceases to be endothermic and becomes exothermic or, stated another way, after the charge stock has contacted the aforesaid 15 to 70 percent of the total catalyst, admixing with the vaporous reactants an amount of hydrogen or bydrogen-containing gases to provide a hydrogen-to-change naphtha mol of at least 8 mols of hydrogen per mol of charge naphtha. (All hydrogen-to-charge naphtha mol ratios being based on the number of mols of naphtha charged to the unit.) The mixture having a hydrogen-tocharge naphtha mol ratio of at least 8 is then contacted with the balance of the particle-form solid platinumgroup metal reforming catalyst in a catalyst-to-charge naphtha ratio to produce C reformate having the required or target octane rating. The vaporous eflluent from the last reforming stage or reactor is cooled to condense C and heavier hydrocarbons, the hydrogen and light hydrocarbons are separated from the condensate to provide reformer gas comprising hydrogen and C to C hydrocarbons at least a portion of which is recycled to the various reforming stages or reactors as described hereinbefore while the condensate is stabilized, and blended, stored, distributed and treated to provide a final product.

I claim:

1. In the method of reforming naphtha in contact with platinum-group metal reforming catalyst in the presence of hydrogen which comprises in a plurality of reforming stages at reforming temperature, pressure, and liquid hourly space velocity contacting platinurmgroup metal reforming catalyst with charge naphtha containing not more than innocuous concentrations of sulfur, nitrogen and arsenic at a substantially constant mol ratio of added hydrogen-to-charge naphtha, separating reformer gas comprising hydrogen and C and C hydrocarbons from conden'sate comprising (3 reformate, and recycling at least a portion of the aforesaid reformer gas to that reforming stage of the aforesaid plurality of reforming stages in which said charge naphtha first contacts the aforesaid catalyst, the predominant reaction in the early stages of the aforesaid plurality of reforming stages being endothermic and in the latter stages of the aforesaid plurality of reforming stages being exothermic, the improvement which comprises regulating the added hydrogen-to-charge naphtha mol ratio to not less than three and not more than seven in those stages of the aforesaid plurality of reforming stages in which the predominant reaction is endothermic and to at least eight in those stages of the aforesaid plurality of reforming stages in which the predominant reaction is exothermic.

2. In the method of reforming naphtha in contact with platinum-group metal reforming catalyst in the presence of hydrogen which comprises in a plurality of reforming stages at reforming temperature, pressure, and liquid hourly space velocity contacting platinum-group metal reforming catalyst with charge naphtha containing not more than innocuous concentrations of sulfur, nitrogen and arsenic at a substantially constant mol ratio of added hydrogen-tocharge naphtha, separating reformer gas comprising hydrogen and C and C hydrocarbons from condensate comprising 0 reformate, and recycling at least a portion of the aforesaid reformer gas to that reforming stage of the aforesaid plurality of reforming stages in which said charge naphtha first contacts the aforesaid catalyst, the predominant reaction in the early stages of the aforesaid plurality of reforming stages being endothermic and in the latter stages of the aforesaid plurality of reforming stages being exothermic, the improvement which comprises regulating the added hydrogen-to-charge naphtha mol ratio to not less than three and not more than seven while said charge naphtha is in contact with the first thirty-five to seventy percent of the total catalyst and to not less than eight while the charge naphtha is in contact with the balance of said catalyst.

3. The method set forth in claim 2 wherein the platinumgroup metal reforming catalyst is distributed in four static beds, wherein the first bed contacted with naptha to be reformed comprises about 3.0 tons and successive beds respectively comprise about 3.0, about 15.7, and about 15.7 tons per 10,000 barrels of naphtha treated per day, wherein the added hydrogen-to-naphtha mol ratio in said successive bed is respectively 3, 3, 6, and 10, and wherein the octane rating of the C and heavier reformate is about 102.

4. The method set forth in claim 2 wherein the platinumgroup metal reforming catalyst is distributed in more References Cited in the file of this patent UNITED STATES PATENTS 2,654,694 Berger et al Oct. 6, 1953 2,902,426 Heinemann Sept. 1, 1959 Evans June 27, 1961 

1. IN THE METHOD OF REFORMING NAPHTHA IN CONTACT WITH PLATINUM-GROUP METAL REFORMING CATALYST IN THE PRESENCE OF HYDROGEN WHICH COMPRISES IN A PLURALITY OF REFORMING STAGES AT REFORMING TEMPERATURE, PRESSURE, AND LIQUID HOURLY SPACE VELOCITY CONTACTING PLATINUM-GROUP METAL REFORMING CATALYST WITH CHARGE NAPHTHA CONTAINING NOT MORE THAN INNOCUOUS CONCENTRATIONS OF SULFUR, NITROGEN AND ARSENIC AT A SUBSTANTIALLY CONSTANT MOL RATIO OF ADDED HYDROGEN-TO-CHARGE NAPHTHA, SEPARATING REFORMER GAS COMPRISING HYDROGEN AND C1 AND C3 HYDROCARBONS FROM CONDENSATE COMPRISING C5+ REFORMATE, AND RECYCLING AT LEAST A PORTION OF THE AFORESAID REFORMER GAS TO THAT REFORMING STAGE OF THE AFORESAID PLURALITY OF REFORMING STATES IN WHICH SAID CHARGE NAPHTHA FIRST CONTACTS THE AFORESAID CATALYST, THE PREDOMINANT REACTION IN THE EARLY STAGES OF THE AFORESAID PLURAITY OF REFORMING STAGES BEING ENDOTHERMIC AND IN THE LATTER STAGES OF THE AFORESAID PLURALITY OF REFORMING STAGES BEING EXOTHERMIC, THE IMPROVEMENT WHICH COMPRISES REGULATING THE ADDED HYDROGEN-TO-CHARGE NAPHTHA MOL RATIO TO NOT LESS THAN THREE AND NOT MORE THAN SEVEN IN THOSE STATES OF THE AFORESAID PLURALITY OF REFORMING STAGES IN WHICH THE PREDOMINANT REACTION IN ENDOTHERMIC AND TO AT LEAST EIGHT IN THOSE STAGES OF THE AFORESAID PLURALITY OF REFORMING STAGES IN WHICH THE PREDOMINANT REACTION IS EXOTHERMIC. 